Note: Descriptions are shown in the official language in which they were submitted.
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Title: Marine structure
The invention is concerned with a marine structure,
suction pile and a method for installing a marine structure.
The invention is particularly, though not exclusively, direc-
ted to the application of so called "minimal platforms".
It is common to position a marine structure pre-assembled
or in seperate parts onto one or more barges or pontoons in a
harbour and then tug said pontoons to the location of destina-
tion, whereafter the structure is lifted from the pontoons
with the aid of a seperate hoisting device and is then the
structure is installed on the subsea bottom with the aid of
that device, wherein prior to or after installing the structu-
re onto the subsea bottom, a foundation therefor is made with
the aid of a seperate foundation pile ramming device.
Suction piles and their way of installing are o.a. known
from GB-B-2300661 and EP-B-0011894, which desclosures are
enclosed here by reference. Briefly, a suction pile is a thin
walled steel cylinder, closed at at least one longitudinal
end, that is located on the subsea bottom with the opposite
end and penetrates the subsea bottom with the aid of a suction
created within the cylinder. The creation of the suction can
be with the aid of a suction source, such as a pump, being on,
or close to or at a distance (e. g. above the water surface,
e.g. at a vessel) from the suction pile. The applied level of
the suction can be e.g. at least substantially constant,
smoothly increase or decrease or else pulsate, for which there
are convenient means; for an e.g. pulsating level a possibly
in the suction pile integrated pressure accumulator that is
intermittendly connected to the inner space of the cylinder.
After use, the suction pile can easily be removed by creating
an overpressure within the cylinder, e.g. by pumping in (se-
a)water.
According to one aspect the invention proposes to make
the marine structure self floating and self foundating by
providing it with buoyancy and one or more suction piles. So
the hoisting device and the foundation plant can be elimina
ted. Preferably the structure has buoyancy of its own, e.g.
obtained by the with the structure integrated appliance that
4D is designed to, once the structure is installed, ballast the
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structure. Buoyancy can also be obtained from the suction
pile, which for that can be provided with a floater. Said own
buoyancy is preferably such that it is substantially contribu-
ting to the required buayancy to make the structure self
floating. It is preferable, if the buayancy can be at least
substantially decreased for installation purposes. By e.g.
filling the one or more floating bodies with ballast, like
water. Therefor it is convenient, to provide the structure
with means for admitting and possibly removing of ballast,
such as between the closed and open position switchable shut-
ter valves in a water supplying respectively water venting
opening to a ballast tank.
Since the structure is self floating and is provided with
one or more suction piles, removal after use is made easier.
On the one hand in that by pressing out the suction pile, the
anchoring of the structure to the underwater bottom can be
removed. On the other hand in that the structure can indepen-
dently rise to the water surface by the (possibly regained)
buoyancy.
The marine structure will typically be relatively small
in this connection, e.g. a production platform with applian-
ces. Because of its own weight, such a marine structure is
designed to be used with a foundation of pile bodies to be
rammed into the ground. Apart from the suction piles, such
marine structure has, preferably, no floating bodies, neglec-
ting parasitic floating bodies like ineviatbly present air
filled spaces, such as frame tubes. The marine structure
referred to here typically will weigh not more than about 50
tonnes.
Now it is no longer necessary to position the marine
structure onto a barge for transport over water. This offers
further advantages since the marine structure does not need to
be lifted from the barge by a hoisting device. If the suction
pile offers at least part of the required buoyancy, the marine
device can be provided with fewer floating structures especi-
ally provided for said purpose, or such floating structures
can even be eliminated.
As such, savings of costs, time, energy, environment and
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materialare possible and one can also work safer.
According to another aspect, the invention proposes to
use the suction pile, or part thereof, as floating body of
which the buoyancy is preferably adapted to keep itself floa-
ting. In this way it is e.g. possible, to take a suction pile
independently floating in to water to its final destination,
so without help of one or more auxiliary floaters. Reclaiming
such a suction pile is also made easier. On the one hand in
that this can free itself independently from the subsea bottom
with its buoyancy, once pressed upwardly but still partly
standing in the subsea bottom. On the other hand since it can
rise to the water surface independently. in particular the
buoyancy of the suction pile according to the invention is
substantially larger than its own weight, e.g. such that the
suction pile alone or in combination with one or more other
suctions piles substantially contributes to the marine struc-
ture with which it is integrated. Accordingly the invention
proposes to provide the suction pile with a convenient buoyan-
cy means.
The buoyancy means can be at least substantially comprise
a space in open communication with the surrounding water at
its under side, such as the pressure space of the suction
pile, e.g. if the suction pile will at least as much upright
as possible float in the water. If one can keep said space
free of water to a satisfying level, the desired buoyancy can
be maintained without requiring to delimit this floating space
at all sides with respect to the water environment. Said space
can therefor e.g. be connected to a convenient means, such as
for delivering a gas generating dry compound into said space,
or for delivering into said space a pressurised gas, such as a
pump, to generate a convenient gas pressure in the suction
space and to possibly maintain it against the pressure of the
surrounding water. Due to the movements of the floating sucti-
on pile in the water, it is expected that without counter
measurements this space will be filled more and more with
water from below. A remedy is to continuously or intermittend-
ly removing of the flowing in water by e.g. refilling said
space with gas, for which said above mentioned means is/are
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continuously or intermittendly activated. In this connection
it is preferred to integrate this means in an active, prefera-
bly automatic, e.g. electronic control circuit wherein said
means is activated in dependency from the detection of the
buoyancy of the suction pile at different times, such as by
measuring e.g. the water level or e.g. the gas pressure
within said space with e.g. a convenient sensor, outputting
its measuring signal to an evaluation device comparing the
measuring signal with an input value, switching on or letting
switching on said means to get back to the initial situation
once a treshold difference value is exceeded.
Application of the above described space in open communi-
cation with its surrounding water has drawbacks in view of
ensuring the buoyancy. Its is therefor preferable if said
buoyancy provides one or more floating spaces that are delimi-
ted at all sides with respect to the water environment and
that are filled with a floating substance, such as air or a
gas or some other material of relatively low specific weight.
Said floating means can comprise e.g. a separate, inflatable,
completely closed, diafragm type floating body, preferably
within the suction pile, e.g. in the suction space. With e.g.
a space of the suction pile that is open at its lower side,
use can be made of an airtight bulkhead with which said ope-
ning can be sealed. If said bulkhead is at least substantially
rigid, e.g. of metal, preferably steel, of sufficient thic-
kness, it can withstand a pressure difference between said
space and its environment by bearing bending stresses, hoop
stresses or a combination of both. Then it is for realising
and maintaining the desired buoyancy not necessary to bring
this space to a pressure that is substantially higher than
atmospheric pressure. If the bulkhead is substantially
flexible, e.g. as an elastic or plastic well formable diafragm
of e.g. rubber, it can be necessary for obtainig and maintai-
ning sufficient buoyancy to bring this space to a pressure
substantially higher than atmospheric pressure.
Concerning a water tight bulkhead at the under side of
the suction pile, one can think of the following structural
embodiments and ways of installing: The bulkhead is pressed
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down by a differential gas pressure within the floating space
onto a bearing projecting inside into the suction pile and
preferably being ring type to ensure sufficient air tightness.
After lowering the suction pile it is position onto the subsea
5 bottom, wherein said bottom raises said bulkhead from its
seat. While the suction pile is sucked into the subsea bottom,
the bulkhead remains in place onto the subsea bottom, such
that the bulkhead eventually arrives close to the top cover of
the suction pile. During pressing out, the bulkhead eventually
comes to rest on its seat near the under side of the suction
pile. The then fast increasing pressure within the suction
pile due to the sealing action of the bulkhead is an indicati-
on that the pressing out is finished.
To bring the floating space to the desired pressure it is
prefered that said space is hermetically delimited. It is then
preferred, to connect the floating space with a convenient
appliance to feed pressurised gas into said space.
The meaning of "delimited at all sides with respect to
the water environment" here is that a boundary with respect to
the surrounding air is not required. The meaning of "hermeti
cally delimited" here is a boundary both with respect to the
surrounding water and the surrounding air.
According to a variant that is preferred at this time,
the tube like shell of the suction pile is extended beyond its
top cover, such that a floating space is present above said
top cover. In this way the lower side of the floating space is
provided by a fixed bottom. To ensure its buoyancy, it is
allowable if said floating space has an open top, unless
during floating e.g. the upper edge of the suction pile comes
below the water surface or waves flush over it. With a view to
ensuring the buoyancy under all circumstances, it is however
preferable, to make said top side water tight, prferably with
a ridig cover. The extension part of the shell can be of the
same structure as the shell part below the top cover. However,
some other design (e. g. smaller wall thickness) could be used
here because of the different mechanical load. This extension
part could be integrated with the suction pile, or be discon-
nectable to be removed from the suction pile after use. The
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wall of the extension part can be in line with the shell wall
of the suction pile below the top cover, but could also have a
larger or smaller diameter. The floating space within the
extension part is preferably connected to a water removing
means, such as a bilge pump, such that incoming water can be
removed. The extension part preferably provides a substantial
lenght part of the suction pile, e.g. about half its length.
At a total length of about 20 meter, the extension part has a
length of e.g. about 10 meter if the extension part and shell
wall of the suction space are in line.
The invention is also concerned with a method of trans-
porting a suction pile over water since it is independently
floating in the water, and a method of transporting a marine
structure over water wherein use is made of one or more sucti-
on piles with buoyancy on which the marine structure is sub-
stantially floating. Apart from the the invention is concerned
with a method of regaining of a suction pile or marine struc-
ture wherein, preferably after pressing out the suction pile
from the subsea bottom, a floating space of the suction pile
is freed from its ballast to get therewith buoyancy such that
the suction pile preferably at least substantially can raise
independently towards the water surface.
Next, the invention is illustrated by way of several non
limiting examples, that are preferred at the moment. In the
drawings is:
Fig. 1 a sectional side view of a first embodiment of the
suction pile according to the invention;
Fig. 2 a side view of a first embodiment of the marine
structure according to the invention, during tug.
Fig. 3 the side view of fig. 2, during lowering;
Fig. 4 the top view of fig. 2;
Fig. 5a-c a prespective view, of an alternative structure
of fig. 2 , during tug ( 5a ) , lowering ( 5b ) and sucking of the
suction pile (5c);
Fig. 6-8 alternatives of fig. 2;
Fig. 9 a top view of fig. 6;
Fig. 10-13 a further alternative of fig. 2;
Fig. 14 still a further alternative of fig. 2;
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Fig. 15a-c a side view of fig. 14.
In fig. 1 the different parts are numbered as follows:
Suction pile 1 (partly embedded into the subsea bottom 2);
shell 3 ( of the suction space 6; diameter 8 m ) ; top cover 4;
open under side 5 (of the suction space 6); suction space 6;
pump 7 ( to get the suction space 6 at a lowered respectively
elevated pressure); connection pipe 8(to communicate space 6
and pump 7); power line 9 (to power pump 7); water surface 10;
floating space 11; shell extension 12.
An alternative is as follows (not shown in the drawings):
The suction pile contains an upwardly movable bulkhead, in
this example a concrete ballast body, suspended from the
suction pile such as with one or more cables or different
flexible or bending stiff pull and/or push members, which
possibly can be shortened and therefore e.g. can be wound onto
an e.g. motoric driven winch. In this embodiment the suction
space 6 and the floating space 11 are combined, which is e.g.
material saving, but also limits the total mass and so the
required buoyancy. A function of this movable bulkhead is to
decrease the free opening at the lower side of the floating
space, such that risc of floating medium (such as air) leaking
through said opening is at least decreased, e.g. by decreasing
the influence of e.g. extern water currents on the inside of
the floating space. In that case the bulkhead can keep a large
clearance with the walls of the floating space, such that e.g.
the risc of wedging during moving up and down of the bulkhead
is at least small. For increased water and/or floatingmedium
tightness, a sealant can be provided between the bulkhead and
walls of the floating space, e.g. of yielding material such as
rubber or elastomer. The bulkhead then also provides a herme-
tic sealed floating space. During floating the bulkhead can
also be flushed by water at merely under side and possibly
sides. However, the indicated water level above the bulkhead
offers extra cushioning of the influence of water currents to
the inside of the floating body.
For lowering it can be advantageous if the buoyancy of
the floating space 11 can be easily removed, e.g. by a conve-
nient means, such as a valve, possibly remotely opened, with
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which at some time water or another ballast means can be
admitted into said floating space and/or floating means (such
as the air or the one or more other gasses) can be vented.
The marine structure according to fig. 2 and 3 has a
platform above the water surface and floating bodies provided
by three suction piles. The platform can be designed for
supporting the exploitation and/or exploration of oil and/or
gas . The platform is a . g. 15 meters above the water surface .
Indicated dimensions are in meters. Each suction pile 1 has an
integrated, preferably rigid ballast body of e.g. concrete, to
e.g. provide stability of the complete structure, in particu-
lar during lowering respectively rising. In this example the
ballast body is located near the level of the bulkhead 4. The
ballast body is supported by the bulkhead 4. The pressure
point is above the centre of gravity. The air valve 13 is
preferably at a high level, the water valve 14 is preferably
at a low level of the floating space 11. The location of the
pump 7 can differ, the same counts for the pipe 8. Although
the struts 15 are flexural stiff elements, particularly tubes,
they can possibly be flexural elements, particularly cables or
equivalent. The struts are each connected to a relevant sucti-
on pile and the riser 16. In top view the suction piles are
located at the corners of a triangle of which the sides are
provided by girder elements 17 fixed to the suction piles. The
suction piles 17 are provided with connecting means 18 for a
tug means 19. The cover 20 of the floating space is spherical.
Air and electricity lines 21 for pumping air into the floating
space respectively controlling the valves 13, 14 and the pump
7 are guided along the struts. During tow the structure is
vertically oriented. The deck can possibly also be installed
onto the mono pile 16 after the suction piles are embedded
into the subsea bottom 2. The platform can possibly be repla-
ced by appliances for oceanografic and/or morfologic measure-
ments, or as navigation beacon, etc.
In fig. 6-8 the situation as installed is shown. The
alternative according to fig. 6 differs from fig. 2 generally
in that the girder elements 17 extend at two different levels
while the struts 15 are connected to the mono pile 16 at a
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lower level. As with fig. 2, the adjacent suction piles 1 are
mutually and each suction pile is fixed to the mono pile 16 by
the girder elements 17 (view also fig. 5).
Fig. 7 shows how the floating space is devided into a
permanent space 11a and a temporary space 11b above. The
temporary floating space 11b can be removed easily, e.g. after
completion of the installation. Again, the buoyancy is concen
trated at the suction piles 1. This embodiment offers more
stability during lowering. During lowering the spaces 11b
maintain their buoyancy for the longest period; that of the
spaces 11a is decreased at an earlier moment in time. The
permanent floating space 11a offers sufficient buoyancy during
tow. For stability during lowering the spaces 11b preferably
project such high, that they still project above the water
surface 10 if the suction piles 1 contact the subsea bottom 2
with the under side. Fig. 8 shows how the temporary floating
space 11b during lowering becomes more and more distant from
the suction piles 1, while those spaces ilb offer buoyancy
during lowering. The spaces 11b are therefor connected to the
structure by extendable pulling elements; in this embodiment
provided by cables 30 extending from a winch 31 via sheaves 32
to the respective spaces 11b. In fig. 7 and 8 the situation
during lowering is indicated with phantom lines. The water
surface during tow is shown in phantom lines.
Fig. 10 shows of an alternative the situation in the
harbour at the cade 40. The structure has maximum buoyancy.
The deck 100 is in a low position. Floating tanks 42 are fixed
below the deck 100 and provide buoyancy (air filled). The
suction piles 1 provide also buoyancy (air filled). The
draught is therewith small.
During tow at full sea (fig. 11) the buoyancy of the
structure is smaller, e.g. for improved stability. In this
case the suction piles 1 provide hardly or no buoyancy.
During lowering onto the subsea bottom 2 (fig. 12), deck
100 and the suction piles 1 are moved apart. The floating
tanks 42 and the suction piles 1 also move apart. The suction
piles are sucked into the subsea bottom 2.
Fig. 13 shows the final situation. The floating tanks 42
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have been removed. The deck 100 is located higher above the
water surface 10. A bearing structure (in this case a "mono
pile") 16 extends from the deck 100 towards the subsea bottom
2. The deck 100 is moved along the mono pile. Said moving can
5 be done by a lifting or jacking system.
The suction piles 1 are maintained in mutual position by
coupling structures 17, and via supporting structures they
bear the bearing structure 16. In the embodiment shown both
elements 15 and 17 are bending stiff inclined respectively
10 horizontal arms. During floating transport the floating tanks
42 are preferably located between said elements 25 and 17.
Fig. 14 shows in side and top view a marine structure
that, once installed, completely disappears in the water
(subsea structure, e.g. template). It is equipped with appli
ances for oil and/or gas production and is connected to an
already drilled production well. The floating tanks 42 are
located in the indicated positions.
Fig. 15a-c shows three different steps for installing the
subsea structure. Firts it is towed (fig. 15a). Next the
ballast tanks 42 are filles, wherein with one or more pulling
cables the stability is ensured (15b). Finally the suction
piles 1 are sucked into the subsea bottom.
The invention also covers embodiments that are developed
by combining one or more aspects of an embodiment described in
here with one or more apects of one or more of the other
embodiments described in here. In this respect a possible
embodiment is wherein the usually open under side of the
suction pile is fluid tight sealed with a bulkhead, while the
suction pile is extended above the top cover, such that the
suction pile has two seperate floating spces and so an increa-
sed buoyancy. According to a further alternative a floating
space can be provided by foam with closed cells, e.g. indivi-
dual globules of styropor with each a diameter of e.g. about 3
mm, with which the suction space could be filled, the purpose
of which is that it is removed, e.g. by pumping, to remove the
buoyancy to e.g. lower the suction pile. Such foam, parti-
cularly if its is sufficient rigid, in combination with a
yielding bulhead, requires no provision and maintaining of an
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over pressure within the floating space. Such rigid foam can
be maintained in position within the floating space by a grid
with sufficient fine mesh, wherein said grid provides e.g. the
boundary with the water of air surroundings. Each foam cell
can be viewed as an hermetically sealed floating space in this
case.
A marine structure with more, e.g. with four, or less
than three suction piles is also feasible.
The invention is also concerned with the application of
the suction pile for providing the foundation of support of a
body, such that the suction pile is exposed to both a load
pressing it into the subsea bottom and a turn, roll or pitch
torque from the supported body. Prior to installation in the
subsea bottom, the suction pile can be irremovably connected
with the structure to be carried, e.g. be connected thereto by
weld joints. However it is preferable from the view point of
e.g. installation, to provide the suction pile with coupling
means allowing afterwards coupling of the suction pile with
the structure to be carried, e.g. after the suction pile is
positioned on the subsea bottom and possibly has lowered
itself into the subsea bottom to the desired depth, or an
intermediate depth. Said coupling means are e.g. one or more
flanges with bolts and nuts, known as such. A more advantage-
ous couling means at the suction pile is adapted to remotely
and/or automatically make the mechanical coupling with the
structure to be supported , e.g. with one or more moving parts
for hooking or snapping together with counter parts at the
structure to be supported, or with one or more parts with
which moving parts at the counter-coupling part of the struc-
ture to be supported can be brought to a load bridging engage-
ment. Such coupling means are e.g. known as such in the field
of load carrying coupling of a marine structure with a pile
rammed into the subsea bottom, which is substantially more
slender than a suction pile and has no provisions to be sucked
into the subsea bottom. The coupling means are preferably
adapted for transmitting a preferably substantial pulling or
pushing force and/or substantial torque. Said torque can come
from a load exerted onto the structure to be supported and
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trying to turn it around an upright and/or one or two orthogo-
nal axes, in respect of which the term rotating moment or
rotating torque, repsectively tilting moment or tilting cou-
ple, respectively pitching moment or pitching torque is used
here. If the suction pile is applied in a single pile founda-
tion with only one suction pile, e.g. for supporting a struc-
ture located under water such as a so called template or
drilling template (mass a.g. 20 tonnes), or a.g. for suppor-
ting a structure extending above water and resting in the
subsea bottom, such as a wind turbine of e.g. 1 MWatt or more,
said coupling means must be adapted both for transmitting
substantial compression forces and substantial tilting, pit-
ching, and rotating moments.
It will be obvious to the skilled person, how strong the
coupling means have to be designed to safely transmit the
compression forces an/or torques. In that case the skilled
person can e.g. find a basis in the coupling between the known
pile rammed into the subsea bottom and the structure to be
supported.
Apart from these coupling means the suction pile can have
appliances for e.g. hoisting of the suction pile or connection
to a suction or pressure source and possibly one or more
valves to selectively close the suction space within the
suction pile.
As such the invention also provides a novel suction pile
with appliances such that it is adapted for supporting materi-
als or devices of equipment of some type and a predetermined
mass of preferably at least about 5000 kg that are used for
all kinds of applications in or above water, indeed or not in
connection with exploitation of minerals such as oil or gas,
e.g. bodies that were until now supported by one or more piles
rammed into the subsea bottom.
The invention offers one or more of the following advan
tageous: ease of use, ease of regaining the suction pile,
cheap installation of the suction pile, possibility of first
installing the foundation and then the body to be supported,
robustness, more reliable foundation, improved bearing of
compression forces and/or rotating or pitch or tilting mo-
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ments/torques such that the foundation can be simplified under
circumstances (e. g. one suction piles in stead of two ramming
piles, e.g. to prevent the structure to be supported from
turning around its shaft), ease of installation due to the
possibility to, e.g., locate the body to be supported onto the
e.g. upright floating or (in shallow water) onto the subsea
bottom positioned or possibly partly into the subsea bottom
penetrated suction pile while subsequently taking the body to
be supported to the desired level since the suction pile
penetrates further into the subsea bottom (and vice versa for
regaining the body to be supported).
It is appreciated that with the novel application the
suction pile, and therewith its coupling means, can also be
exposed to a tension load, e.g. from the body to be supported
and/or since the suction pile also serves as an anchor for
some different, non-bearing body.
So the invention is according to the enclosed claims.
